stone on the road

"In ancient times, a king planted a stone on the road with his soldiers. He then hid in the bushes and watched to see if anyone would remove the stone from the path. The king's richest merchants and courtiers passed by and kept walking around it.
 
Many people accused the king of not keeping the roads clean, but none of them did anything to remove the stones from the road.
 
One day a farmer came with vegetables. As he approached the rock, the farmer lowered his load and tried to remove the rock from the path. After much pushing and shoving, he finally gave up

When the farmer returned to get his vegetables, he saw a purse lying in the street where the first stone had been. There were lots of gold coins in the purse, and King noted that the gold was for the man who had removed the stone from the road.